System and method for derivation and real-time application of acoustic v-path correction data

ABSTRACT

A system and method for carrying out non-destructive testing and inspection of test objects to assess their structural integrity uses a calibration module configured to provide V-Path time of flight (TOF) correction data over a plurality of object thickness points, obtained from an object or objects having known thicknesses using the same physical probe as is used for the inspection measurements. When a probe launches acoustical waves into a test object and an instrument and a control system compute a time of flight value of the acoustical waves launched by the probe, the pre-obtained V-Path TOF correction data is used to correct the measured time of flight computed by the instrument.

FIELD OF THE INVENTION

The present invention relates to non-destructive testing and inspectionsystems (NDT/NDI) and more particularly to a method to compensate foracoustic V-Path time of flight errors and thereby optimize inspectionmeasurement accuracy.

BACKGROUND OF THE INVENTION

The measurement data from NDT/NDI devices used for the routinemonitoring of structural integrity must be of sufficient accuracy toallow a valid assessment to be made of the condition of the structureunder test. Examples of such structures are pipes and vessels widelyused in the petrochemical and other industries. Examples of measurementdata are pipe wall thickness and other geometric conditions, including,but not limited to, the presence of irregular surfaces (e.g. corrosion,oxide, etc.) and flaws (e.g. porosity, cracks, etc.).

The decision to perform or not perform maintenance on a structure ismade based on the assessment of the measurement data. Therefore, themeasurement accuracy will have a direct impact on the decision. Theconsequence of inaccurate measurement data that underestimates anunfavorable condition of a structure can result in failures occurringbefore maintenance is performed. Conversely, inaccurate measurement datathat overestimates an unfavorable condition of a structure can result inperforming expensive and unnecessary maintenance.

One of the most common NDT/NDI devices used for assessing structuralintegrity is a corrosion gage, such as the instant assignee's 37 DLPproduct. Products of this type typically employ a ‘dual-element’ probeor probe system that contains one element for acoustic transmission andanother for acoustic reception, preferably packaged in an integralhousing. The two elements are set at a fixed angle, thereby setting afixed focal depth and ‘V-Path’ within the object being tested. Althoughthis element positioning provides advantages for measuring corrosionwear, measurement errors, known as ‘V-Path errors’, can be introducedwhen measuring thicknesses at depths other than that of the focal depth.

The specific challenge herein dealt with is to provide a method thatwill ameliorate the measurement errors resulting from V-Path echo, whichis the energy path traveled by the acoustic wave after the energy istransmitted into the target material and reflected from the back-wall ofthe material and into the receive element of the transducer.Particularly, V-Path errors occur when thickness measurements are beingmade on a material thinner than the focal thickness of the transducer.

Existing efforts have been made to eliminate or reduce such errors asdescribed above. Thus, embodiments employing pre-defined data for theV-Path, or time distortion, correction in the calculation of a thicknessmeasurement are well known by those skilled, and are therefore notdescribed in detail herein.

One conventional solution for V-Path error compensation employspre-defined static data tables to compensate for the time distortion;however, this solution has the drawback of not accounting for actualmaterial sound velocity, transducer wear and manufacturing variances intransducer population.

Materials under inspection have their own individual velocities denotedas V, where V=material velocity. U.S. Pat. No. 3,554,013 teaches ahardware error correction circuit for ultrasonic thickness gauges. It isnot a software method and presents the drawbacks of thermal and otherelectronic drift and material costs.

U.S. Pat. No. 4,570,486 teaches V-Path calibration for UT thicknessmeasurement using hardware error correction circuits for ultrasonicthickness gauges. It is not a software method and presents the drawbacksof thermal and other electronic drift and material costs.

Current V-Path methods using a pre-determined data table, called “V-PathTable,” use empirical methods of deriving data to generate the Table.The predetermined Table is generated by using TOF measurement methods ona batch of typical transducers of one model. It is then used forhundreds of the transducers of the same model for many years. Theexisting V-Path Table is herein referred to as the “Empirical V-PathTable”.

Using an Empirical V-Path Table to compensate all the transducers of onemodel is less accurate because of variations of transducer factors suchas acoustical focal depth and saturation of the acoustic barrier. Thefactors causing such variations include manufacturing tolerance changesin different batches of transducers, changes in materialcharacteristics, and changes caused by wear-and-tear.

Accordingly, a solution that overcomes the drawbacks described above andresults in advantages highly valued by potentially affected industrialand public infrastructure concerns, needs to:

-   -   a. Improve measurement accuracy;    -   b. Extend the longevity of transducers along with their        measurement accuracy; and    -   c. Improve measurement accuracy of generic transducers for which        the pre-defined V-Path data is unknown.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide asystem and method for obtaining more accurate V-Path correction data.

It is a further object of the invention to provide a system and methodthat is able to extend the longevity of proprietary transducers andtheir measurement accuracy.

Yet another object of the invention is to provide a system and method toimprove measurement accuracy of generic transducers for which apre-defined V-Path correction data is unknown.

The foregoing and other objects of the invention are realized with athickness measuring system for measuring the thicknesses of testobjects. The system includes a calibration module which is configured toprovide V-Path time of flight (TOF) correction data over a plurality ofobject thickness points, obtained from one or more objects having knownthicknesses. A probe configured to launch acoustical waves into a testobject and to receive returning waves is employed, to produce anelectrical output representative of the returning waves. An instrument,including control and computation hardware and software, is coupled tothe probe and is configured to compute a time of flight value of theacoustical waves launched from the probe. A correction module associatedwith the instrument and configured to receive the V-Path TOF correctiondata from the calibration module is used to correct the time of flightcomputed by the instrument, based on the V-Path TOF correction dataprovided by the calibration module.

In accordance to various embodiments of the system and method of thepresent disclosure, the probe is preferably a dual element probe.Further, the V-Path TOF correction data can be provided in the form of aplurality of discreet correction values and those values can be used tocompute correction values, needed to correct the TOF in real-time as themeasurement is being made. Alternatively, linear equations or higherorder polynomials can be fitted to the V-Path TOF correction data andthese equations can be used to compute the needed TOF correctioninformation in real-time as the measurement is being made.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a Dual Element Ultrasonic Transducer depictingthe Effective Angular Sound Energy Path for Thick Material targets afterthe Transducer has been electrically excited by the UT apparatus.

FIG. 2 is a diagram of a Dual Element Ultrasonic Transducer depictingthe Effective Angular Energy Sound Path for Thin Material targets afterthe Transducer has been electrically excited by the UT apparatus.

FIG. 3 is a diagram showing the Measured Time Intervals that comprises aTime Of Flight measurement for a Dual Element Ultrasonic Transducer.

FIG. 4 is a diagram showing the functional modules used for deriving andemploying ultrasonic V-Path correction data according to the presentinvention.

FIG. 5 is a module or component embodiment showing the module and stepsrequired for acquiring input calibration data from the operator.

FIG. 6 is a module or component of the embodiment showing the module andsteps required for deriving and creating the User Created V-Pathcorrection values.

FIG. 7 is a module or component of the embodiment showing the module andsteps required for the application of the V-Path correction data duringthe measurement calculation phase.

FIG. 8 is a chart showing the Actual Thickness vs. the MeasuredThickness by an UT apparatus, and the associated calibration points ofthe embodiment.

FIG. 9 is a chart showing a plot of time correction factors at differentmeasured wave flight times.

DETAILED DESCRIPTION OF THE INVENTION

In order to assist the understanding of presently disclosed V-Path errorcalibration method, the following description is given in associationwith background FIGS. 1-3.

It should be noted that ‘sensor’, ‘probe’ and ‘transducer’ are hereinused in the present disclosure interchangeably. The term ‘real-timemeasurement’ is used in the present disclosure to mean the immediatemeasurement result provided to the user or external device bymeasurement device 111 (FIGS. 1 and 2) using one or more probeexcitation/response cycles. The measurement result may be provided tothe user by means of display 111 b, an integral audio device (notshown), and/or an external device by means of input/output port 111 a.The measurement result may be comprised of, but not limited to, valuesrepresenting thickness, relative thickness and/or an alarm indication.

Referring to FIG. 1, the presently disclosed V-Path error compensationmethod as disclosed in used in conjunction with a dual-elementtransducer ultrasonic inspection system. The inspection system comprisesa transducer 102; a measurement device 111 wherein the algorithm of thepresent disclosure is executed; and a target test object 107.

The invention is a system and method employing a software program thatmay be used for producing, and employing time distortion correctiondata, henceforth referred to as a V-Path Table for probes, that may beemployed by ultrasonic thickness measuring apparatus. Ultrasonicthickness measuring apparatus will henceforth be referred to asmeasurement device 111. It should noted that although the preferredembodiment of the present disclosure describes an exemplary ultrasonicmeasuring apparatus, the teachings of the present disclosure may beapplied at acoustic frequencies below the ultrasonic range (typically<20 kHz).

V-Path correction data may be used in the measurement calculation whenthe need to compensate for time distortion introduced by Angular SoundEnergy Paths is required. Refer to the Effective Angular Sound EnergyPaths 108 in FIG. 1 and FIG. 2. Note that the effective Angular SoundEnergy Path distortion is greater in thin material targets 207 FIG. 2,than that of thick material targets 107 of FIG. 1. Thus, as shown bycurve 802 of FIG. 8, time distortion effects increase as the thicknessof the target material decreases when V-Path correction is not present.Hence, the application of V-Path correction factor, t_(v), (of Eq. 1below) may be essential for accurate thickness measurement in thinmaterial targets.

Referring again to FIG. 1, the Transmit Element side of the Transducer101 generates an ultrasonic energy wave after being excited byelectrical signals at its Input Connector 105 by measurement device 111.The Ultrasonic Energy Wave will hereby be referred to as Wave.

Referring to FIG. 3, the Wave 108 generated by the Transmit Element 101,travels through the Transmit Delay Material 100 and into the coupledtarget material, such as 107 or 207, through front-surface 110. The Waveis then reflected from the coupled target back-surface 109 and backthrough front-surface 110 and Receive Delay Material 106 into theReceive Element 104, where it is converted back to an electrical signal.

As can be appreciated by those skilled in the art, the measurementdevice 111 is capable of precisely measuring the Time Interval (TI)comprised the Time Of Flight (TOF) of each of the elements depicted inFIG. 3, i.e., T1, T2, T3, and T4. It should be noted that the TImeasurements associated with T1 and T4 are typically made whentransducer 102 is decoupled from the target material and element 101 and104 are each operated in pulse-echo mode to measure the TI to and fromtheir respective transducer contact surfaces 101 a and 104 a.Accordingly, the TI values T2 and T3 associated with the target materialmay be measured because the T1 and T4 are TI components of the total TOFare accounted for.

Therefore, the ‘thickness’ calculation H for a target material, whetherit be a calibration block or test object, may be calculated by Eq. 1 asshown below,

H=[(TI+t _(v))V]/2  [Eq. 1]

where,

TOF=T1+T2+T3+T4

t_(x)=T1+T4

TI=TOF−t_(x)

t_(v)=V-Path correction factor

V=sound velocity in test blocks 107 and 207.

It should be noted that the above equations are also used to generatethe Empirical V-Path Tables typically provided by transducermanufacturers. An Empirical V-Path Table is usually provided for aspecific transducer model number.

The preferred embodiment of the present disclosure is a system andmethod employing a software program that may be used for producing, andemploying time distortion correction data in real-time, henceforthreferred to as ‘V-Path Table’ for Transducers that may be employed byultrasonic thickness measuring apparatus. A key aspect of the presentinvention includes deriving an ‘User Created V-Path Table’ and employingsuch for dual-element transducer calibrations and test objectmeasurement. As further described below, it should be noted that incomparison with the existing Empirical V-Path Table, ‘User CreatedV-Path Table’ is derived using TOF data measured for a specific physicaltransducer. The following method/software program can be used togenerate the ‘User Created V-Path Table’ on any specific transducer andat any point during the service life of the transducer.

As shown in FIG. 4, the presently disclosed method in combination with asoftware program performs process 400 that is comprised of modules (orsteps) including Setup and Calibration Data Acquisition 500, UserCreated V-Path Table Creation 600, and Creation and Output ofCompensated Value H 700.

Referring now to FIGS. 4, 1 and 2, in step 500, transducer 102 iscoupled to a calibration block such as 107 or 207, to acquire therequired data elements for the creation of the V-Path table in step 600.Next, in step 700 the V-Path Table is employed during real-timemeasurement acquisition to correct for time distortion, therebyresulting in a compensated thickness measurement value H. It should benoted that process 400 is performed within inspection device 111 whenconnected to transducer 106.

It should be noted that the combined ‘steps’ above are also calledmodules. The present disclosure is focused on a combination of asoftware program and a method. The terms ‘Step’ and ‘module’ areinterchangeably used, wherein ‘step’ is used in the context of themethod and ‘module’ is used in the context of the system and associatedsoftware program.

Turning now to FIG. 5, which provides a more detailed description of themodule 500, note that the operator is required to perform a calibrationon a range of blocks of different thicknesses. The range or number ofthickness points is determined by the operator. After the Setup andCalibration Data Acquisition process within module 500 is completed, theresulting data is provided to the module 600 of FIG. 6 to derive theV-Path Table. The data in the V-Path Table is then used in module 700 ofFIG. 7 wherein it may be utilized in the calculation of compensatedmeasurement H to yield an accurate thickness as shown in Eq. 1.

It should be noted that the term “actual” as used in the presentdisclosure denotes the precise metrics of the target material, and theterm ‘measured’ denotes the metrics of the target material acquired bythe measurement device 111. In step 502, the operator couples thetransducer 102 to the calibration block and enters the actual thicknessof the block in step 503. The actual TI is then calculated in step 504using Eq. 2 shown below.

ActualTI_(i)=[ActualThickness_(i) /V]*2  [Eq. 2]

where,

V=Material Velocity of the block

The measurement device 111 then acquires the TI in step 505 (FIG. 5),where the measured time is calculated using Eq. 3 shown below.

MeasuredTI_(i) =T2+T3  [Eq. 3] (see FIG. 3)

The measured thickness is calculated in step 506 by Eq. 4 shown below.

MeasuredThickness_(i)=[MeasuredTI_(i) *V]/2  [Eq. 4]

where

V=Material Velocity of the block

The data obtained for ActualTI_(i), ActualThickness_(i), MeasuredTI_(i)and MeasuredThickness_(i) are then stored into CalData[i] in step 507,as multiple-element array or array of data structures. The procedurerepeats steps 502 through 508 until the desired range of calibrationthicknesses have been entered. The module in FIG. 5 is completed in step509.

Reference is now made to FIG. 6, wherein detailed steps of module 600are elaborated. The CalData[i] data structure is preferably sorted fromsmallest ActualTI_(i) value to largest ActualTl_(k) value in step 602,where k is the number of calibration points entered in step 510 of FIG.5. Once sorted, a time correction factor is calculated for eachcalibration point by Eq. 5 shown below.

t _(c) [i]=ActualTI[i]−MeasuredTI[i]  [Eq. 5]

In practice, t_(c)[i] and MeasuredTI[i] are stored in step 604 intoVPathData[i], which is a multi-element array or array of datastructures. The process of calculating t_(c)[i] and storing it alongwith MeasuredTI[i] in steps 603 through 606 continues until i=k, where kis the number of calibration points entered in step 510.

Module 700 is now described with reference to FIG. 7. The “User CreatedV-Path Table” was created as described above within the software programmodules 500, and 600, and is then used in module 700 to compensate fortime distortion in the thickness measurement of the measurement device111 and thereby produce V-Path compensated measurement value H.

For module 700, the operator couples the Transducer to the materialunder test in step 702 and the measurement device 111 acquires a timemeasurement LiveTI in step 703 using Eq. 6 shown below.

LiveTI=T2+T3  [Eq. 6] (see FIG. 3)

LiveTI is then utilized to determine an index n into VPathData[ ] instep 704 for selecting the appropriate data in the table for thatthickness and then using the data for deriving the live (real-time)V-Path correction factor, t_(v) in step 705 using Eq. 7 shown below.

t _(v) =ΔT1+(LiveTI−T1)*[(ΔT2−ΔT1)/(T2−T1)]  [Eq. 7]

and referring to FIG. 8,

T1=VPathData[n].MeasuredTI, the MeasuredTI value in VPathData[n].

ΔT1=VPathData[n].t_(c), the t_(c) value in VPathData[n].

T2=VPathData[n+1].MeasuredTI, the MeasuredTI value in VPathData[n+1].

ΔT2=VPathData[n+1].t_(c) the t_(c) value in the VPathData[n+1].

Finally, V-Path compensated measurement value H of the target object iscalculated in step 706 by using Eq. 8 shown below.

H=[(LiveTI+t _(v))*V]/2  [Eq. 8]

FIG. 8 shows time correction factors designated as ΔT1, ΔT2, etc., atspecific calibration points, plotted against the thickness of the testobject. It also shows time correction factors for live measurements andidentifies them as LiveTI. These “A” designated time correction factorscan be plotted as shown in FIG. 9, as specific (x,y) coordinate pointswhere, in FIG. 9, the ordinate (y-axis) indicates the time correctionfactors, at each of the calibration points. The x-axis designates themeasured TOF (Time of Flight), at the calibration points.

In the preceding embodiment, time correction factors for the livemeasurement points are obtained via interpolation calculations, aspreviously described. See, for example, equation 7. Those skilled in theart appreciate that the plot (FIG. 9) of the actual time correctionfactors, relative to the measured times at the calibration points,produces a non-linear function, which is not easily fitted to a rigidmathematically expressed formula.

However, in accordance with the presently described alternativeembodiment, the software system of the present invention aggregatesthese discrete data points, for example, between points A and B; B andC; C and D; and D and E, and produces a linear transfer function(formula) for each such section. This allows calculation of the Δ timecorrection factors, for live measurements, using a specific equation foreach section.

Thus, for the Section A-B, the transfer function, i.e. the formula, forcalculating the correction factor for the TOF obtained on a test objectmay be expressed as: Δy_(A-B)=f(Δx); according to a general form of theequation, which is y_(A-B)=−A(x)+B, with A and B being constants whichare unique to each of the sections A-B; B-C; etc., in FIG. 9. Thevariable “x” is the live measured TOF obtained during a test. By addingthe thus obtained Δy to the live TOF measurement, one obtains a TOF forthickness values falling on and between the discrete time correctiondata points, which readily allows calculating the thickness parameterbased on the acoustical wave speed through the test object.

The approach of this embodiment does not require accessing the V-Pathdata tables and calculating interpolated corrections during livemeasurements on test objects. Instead, it allows the use of directconversions, using the above formulas.

In creating the segmentized linear transfer functions shown in FIG. 9,it should be noted that the software of the present invention usesactual measurement data to determine the starting and ending points foreach section of the curve, using well known mean deviation methodologiesto enable the fitting of a linear equation over the selected dataranges.

In operation, a TOF measurement is taken. Then, it is determined towhich linear segment the measurement TOF value belongs. Lastly, theappropriate equation is used to calculate the TOF correction. As notedabove, the calculation of the thickness is then readily obtained.

In an alternate embodiment, V-Path correction data may be determined fora specific physical transducer by some other means than the measurementdevice 111 and provided to the measurement device 111 to conduct V-Pathcorrection during real-time measurements. One of the other means may bea measurement device 111 other than the one that will be used to conductthe real-time measurements.

In another alternate embodiment, as shown in FIGS. 1, 2 and 3, ID 112may provide a means of physical probe identification (i.e. a ‘probeidentifier’), such as a serial number, coupled to measurement device 111to be used to recall from its memory the V-Path correction data tableassociated with the probe identifier. ID 112 may be a non-volatile (NV)digital memory device or a component that maintains a substantiallyconstant value over time—such as a resistor. ID 112 is preferablypackaged in an integral manner with probe 102 in order to ensure that ID112 remains with the probe. For example, ID 112 may be packaged with theprobe, the probe cable assembly, or any other device attached to probe102 on a permanent or semi-permanent basis.

If ID 112 is a NV digital memory device of adequate capacity, the V-Pathcorrection data table may be stored with the physical probe it appliesto (i.e. ‘V-Path stored in probe’), thereby allowing the probe to beused with any measurement device 111 without the need for themeasurement device 111 to store a database of V-Path correction datatables associated with probe identifiers.

The primary advantage provided by the ‘probe identifier’ and ‘V-Pathstored in probe’ embodiments is improved inspection process efficiencyby eliminating the need to perform the V-Path correction data tablecalibration process before starting an inspection measurement session.

Although these embodiments are described in relation to a V-Pathcorrection data table associated with a specific physical probe, V-Pathcorrection data may also be created by empirical means, such asderivation from a sample population of probes. Analytical means may beused as well, such as a mathematical model of a distinct probe type.

It should be noted with respect to these embodiments that the V-Pathcorrection data table stored in the NV digital memory device may beupdated by the user from time to time to account for changes in physicalprobe properties, thereby maintaining optimal accuracy of the V-Pathcorrection data.

Other arrangements of embodiments of the invention include softwareprograms to perform the method embodiment steps and operationssummarized above and disclosed in detail below. More particularly, acomputer program is one embodiment that has a computer-readable mediumincluding computer program logic encoded thereon that when encoded andexecuted in a computerized device provides associated operationsproviding V-Path error calibration as explained herein. The computerprogram logic, when executed on at least one processor with a computingsystem, causes the processor to perform the operations (e.g., themethods and algorithms) indicated herein as embodiments of theinvention. Such arrangements of the invention are typically provided assoftware, code and/or other data structures arranged or encoded on acomputer readable medium such as but not limited to an optical medium(e.g., CD-ROM, DVD-ROM, etc.), floppy or hard disk, a so-called “flash”(i.e., solid state) memory medium, or other physical medium, such as butnot limited to firmware or microcode in one or more of ROM or RAM orPROM chips, or as an Application Specific Integrated Circuit (ASIC) oras downloadable software images in one or more modules, sharedlibraries, etc. The software or firmware or other such configurationscan be installed onto a computerized device to cause one or moreprocessors in the computerized device to perform the techniquesexplained herein as embodiments of the invention. Software processesthat operate in a collection of computerized devices, such as in a groupof data communications devices or other entities may also provide thesystem of the invention. The system of the invention may be distributedbetween many software processes on several data communications devices,or all processes may run on a small set of dedicated computers, or onone computer alone.

It is to be understood that embodiments of the invention may be embodiedstrictly as a software program, as software and hardware, or as hardwareand/or circuitry alone. The features disclosed and explained herein maybe employed in computerized devices and software systems for suchdevices such as those manufactured by Olympus NDT Inc. of Waltham, Mass.

Although the present invention has been described in relation toparticular exemplary embodiments thereof, many other variations andmodifications and other uses will become apparent to those skilled inthe art. It is preferred, therefore, that the present invention not belimited by the specific disclosure.

1. A thickness measuring system for measuring thicknesses of testobjects, comprising: a probe configured to launch acoustical waves intoa test object, to receive returning waves and to produce an electricaloutput representative of the returning waves; a calibration moduleconfigured to provide V-Path time of flight (TOF) correction data over aplurality of object thickness points, obtained from one or more objectshaving known thicknesses, using the same physical probe as is used forsaid measuring; a control and computation unit, coupled to the probe andconfigured to compute a time of flight value of the acoustical waveslaunched by the probe; and a correction module associated with the unitand configured to receive the V-Path TOF correction data from thecalibration module and to correct the time of flight computed by theunit based on the V-Path TOF correction data provided by the calibrationmodule.
 2. The thickness measuring system of claim 1, in which the probeis a dual element probe.
 3. The thickness measuring system of claim 1,in which the V-Path TOF correction data is provided in the form of aplurality of discrete correction values, and wherein the unit isconfigured to correct the measured TOF value by locating a correspondingdiscrete TOF correlation data and/or by computing a correction TOF databy interpolation using adjacent ones of V-Path correction data.
 4. Thethickness measuring system of claim 3, in which an object thickness H ofthe test object is obtained using the following equations:H=[(LiveTI+t _(v))*V]/2Wheret _(v) =ΔT1+(LiveTI−T1)*[(ΔT2−ΔT1)/(T2−T1)] WhereT1=VPathData[n].MeasuredTI ΔT1=VPathData[n].t_(c)T2=VPathData[n+1].MeasuredTI ΔT2=VPathData[n+1].t_(c) Wheret _(c) [n]≦LiveTI<VPathData[n+1]·MeasuredTI
 5. The thickness measuringsystem of claim 1, in which the V-Path TOF correction data for eachobject thickness are obtained by repeated measurements and by theaveraging of repeated measurements at the same thickness.
 6. Thethickness measuring system of claim 1, wherein the corrected times offlight are derived from linear equations which are fitted to the V-PathTOF correction data.
 7. The thickness measuring system of claim 1,wherein the calibration module comprises a data table.
 8. The thicknessmeasuring system of claim 1, wherein the system is configured to performnon-destructive testing to monitor the structural integrity of the testobjects.
 9. The thickness measuring system of claim 1, including TOFprobe identification data of said probe and a memory storing multipleTOF correction data for a plurality of probes, each TOF correction databeing identified by a corresponding TOF probe identification data. 10.The thickness measuring system of claim 1, including a memory integratedwith said probe which stores said TOF correction data therein.
 11. Amethod of measuring the thicknesses of test objects, comprising:launching acoustical waves into a test object with a probe and receivingreturning waves and producing an electrical output representative of thereturning waves; collecting and providing V-Path time of flight (TOF)correction data over a plurality of object thickness points, andobtaining the same from one or more objects having known thicknesses,using the same physical probe as is used for said measuring; computing atime of flight value of the acoustical waves launched by the probe; andusing the V-Path TOF correction data and correcting the time of flightthat has been computed, based on the V-Path TOF correction data obtainedrelative to the objects having known thicknesses.
 12. The method forclaim 11, further including providing the V-Path time of flightcorrection data in the form of a plurality of discreet correction valuesand using interpolation to correct the time of flight computed for thetest object.
 13. The method of claim 11, including calculating an objectthickness H of the test object using the following equations:H=[(LiveTI+t _(v))*V]/2Wheret _(v) =ΔT1+(LiveTI−T1)*[(ΔT2−ΔT1)/(T2−T1)] WhereT1=VPathData[n].MeasuredTI ΔT1=VPathData[n].t_(c)T2=VPathData[n+1].MeasuredTI ΔT2=VPathData[n+1].t_(c) Wheret _(c) [n]≦LiveTI<VPathData[n+1]·MeasuredTI
 14. The method of claim 11,including obtaining the V-Path TOF correction data for each objectthickness by repeated measurements and by averaging the repeatedmeasurements at the same thickness points.
 15. The method of claim 11,including calculating the corrected times of flight from linearequations which have been pre-fitted to the V-Path TOF correction data.16. The method of claim 11, including performing non-destructive testingof the test object to monitor the structural integrity thereof bymeasuring the thickness of the test object at various locations thereon.17. The method of claim 11, further including obtaining the V-Path TOFcorrection data by reading TOF probe identification data associated withsaid probe being used, and selecting said V-Path TOF correction dataassociated with said probe from a memory containing V-Path correctiondata for a plurality of probes.
 18. The method of claim 11, includingstoring said V-Path TOF correction data in a memory module integratedwith said probe.
 19. A method of measuring the thicknesses of testobjects, comprising: launching acoustical waves into a test object witha probe and receiving returning waves and producing an electrical outputrepresentative of the returning waves; collecting and providing V-Pathtime of flight (TOF) correction data over a plurality of objectthickness points, and obtaining the same from one or more objects havingknown thicknesses, using one or more probes having characteristicssimilar to said probe used for said measuring; computing a time offlight value of the acoustical waves launched by the probe; and usingthe V-Path TOF correction data and correcting the TOF value that hasbeen computed, based on the V-Path TOF correction data obtained relativeto the object or objects having known thicknesses.